Definition 1.2.2: Function, Domain, and Range

Let A and B be two sets. A functionf
from A to B is a relation between A and B such
that for each aA there is
one and only one associated bB.
The set A is called the domain of the function, B is
called its range.

Often a function is denoted by y = f(x) or simply f(x),
indicating the relation { (x,f(x)) }.